1. Field of the Invention
The present invention generally relates to an arrangement for, and a method of, enhancing image projection, especially for use in a color image projection system.
2. Description of the Related Art
It is generally known to project a two-dimensional image on a projection surface based on a pair of scan mirrors which oscillate by respective drives in mutually orthogonal directions to scan a laser beam over a raster pattern. One of the scan mirrors, sometimes referred to herein as an X-mirror, is driven at a faster rate to reflect the laser beam along a scan direction and generate a scan line. The other of the scan mirrors, sometimes referred to herein as a Y-mirror, is driven at a slower rate to reflect the scan line along a transverse direction perpendicular to the scan direction. The drive for the Y-mirror oscillates the Y-mirror in one direction about an axis at a constant drive speed during a forward scan, that is from an upper scan line to a lower scan line of the raster pattern, or vice versa. The drive for the Y-mirror does not drive the Y-mirror in the opposite direction about the axis during a return scan, that is from the lower scan line to the upper scan line of the raster pattern. Instead, the Y-mirror is self-returnable at a mechanical resonant frequency during the return scan, sometimes referred to herein as a drive-unassisted flyback.
Although generally satisfactory for their intended purpose, the images projected by the known image projectors could be enhanced. Sometimes a drive cycle of the Y-mirror, that is the total duration of the forward scan and the return scan, does not exactly equal a frame rate or period of an incoming video signal. The video signal can have a variable or an unstable frame rate, and a lack of synchronization between the video signal and the Y-mirror drive signal can lead to distorted images.
Another problem with known image projectors is that the lasers, which emit the laser beams, have a non-linear modulation function which can also change with temperature, age and other factors. Such lasers need to be calibrated because the image projectors require a linear and stable relationship between laser output power and the incoming video signal.
Yet another problem with known image projectors is that the Y-mirror deviates from its ideal speed profile over time. Such speed deviation needs to be corrected to insure that the projected image is of high quality.